Looking at putting together a 5.56 caliber PDW for use out to 100-150 yds. Excluding the Sig MCX. What barrel length would you recommend? I'm looking at 8.5" and 10.5" uppers,and a lower with the SB Tactical PDW brace. Pics would be appreciated. I also want it to fit in a covert bag or pack.

James

Here are my 8.5" and 10.5 inch. They are DI not piston.

The 8.5 is easiest to conceal in a small bag and its 22" long. Its fun to shoot but I don't recall its crono speed.

The 10.5 is my favorite. Its 26" long and needs a taller backpack or bag. I have a longer suppressor mount on this one so its a bot longer. It cronos around 2400 fps with 55 grain 556.

gw3971

Is that the Maxim Defense Stock on the 10.5" ?
Is it comfortable to shoot?

Yep. They are both Maxim. They are very comfortable to shoot.

Wow BCM is finally making a 10.5? Sweet! Finally.

quote:

Originally posted by Veeper:
Wow BCM is finally making a 10.5? Sweet! Finally.

11.5” is be smallest BCM will go.



Here is a Q and A from Paul from BCM

Why doesn't BCM make a 10.5" upper?
ETA -

Q: Why BCM chose the 11.5" SBR over the 10.5"

I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.

First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.

A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)

If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".
The BCM 11.5" Runs Like a Dream.

Hope this info helps,
Paul


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Paul from BCM posted on TOS

That makes a lot of sense. Is it possible to get under the 26" (I think) pistol max some states have with 11.5?

OP - Sorry I'm grifting your thread....

I have an Adams Arms 7.5” piston upper that I put on a SBR’d lower from time to time. Other than being stupid loud there’s not a problem with it. Runs significantly cooler than my 10.5” DI upper

I personally don’t like the ballistics of 5.56 in short barrels, so I would vote at least 10.5”.

For a shorter barrel, I’m a big fan of 300 blk. I know you said you don’t want an MCX, but the rattler is ideal for what you’re describing. I would try to make a piston AR close to that.

5” 300blk with a folding thin stock will be much smaller than a 10.5” barrel 5.56.

been using a brn-180s on a pistol lower. runs suppressed without issue, has a gas adjustment for it. gas blowback while suppressed is better than any ar upper i have. disassembly for cleaning is pretty easy too. dont think it has the numbers sold yet to get a good consensus on reliability and quality. only my sample of 1 seems fine.

any folding brace adapter will work as it does not need a receiver extension/buffer tube.

Short PDWs is a place 300BLK can shine over 556.

I haven't done it thought, it's either a CZ Scorpion in 9mm or a SBR SCAR 16.

Folding stock / brace helps over the standard AR15 buffer tube format for getting a compact PDW.

Q Honey Badger would be another recommendation. 7" 300blk with a PDW (more compact) stock, or even a pistol brace option.

Why piston? What are the goals of the gun?

If you're looking to use it for defense, as an actual PDW, I would caution against both a piston and barrel under 10.5" in 5.56.

RHINOWSO

Would a 8"upper for 300 Blackout be too short to suppress . I'm looking at a pdw for home defense in a apartment. Or would a 10" 300 Blkout upper be better? If I wanted to stay with 5.56 would 10.5" or 11" upper be better?


James

My 10.5" pistol clocks PMC factory 55 FMJ's at 2550 ish on average(suppressed). Hand loaded 55 FMJ's with a pull down ball powder and magnum primer averaged just shy of 2600 fps. The PMC had nice SD numbers(5 shot SD of 10 or less) and is softer in recoil, though pretty dang dirty. Same barrel length in a 300 BLK 10.5 has been accurate and you all probably know how many different bullets these can use. Subs are a rabbit trail all their own

quote:

Originally posted by depusm12:
Would a 8"upper for 300 Blackout be too short to suppress . I'm looking at a pdw for home defense in a apartment. Or would a 10" 300 Blkout upper be better? If I wanted to stay with 5.56 would 10.5" or 11" upper be better?

Much depends upon the suppressor's construction and how the manufacturer's rating. A 300blk-specific can with aluminum parts may not take kindly to an SBR with supersonic ammo. A steel/titanium can rated for 308 or 300WM will likely have no issues with even the shortest 300blk barrel with supersonic ammo. Subsonic 300blk ammo is rarely an issue with cans -- even with the shortest of 300blk barrels.

Even with a good suppressor, a shorter barrel produces a louder crack than a longer barrel with supersonic ammo.

Longer barrels produce greater muzzle velocity, and as a result, greater muzzle energy. The velocity/energy equation depends on the ammo and the barrel -- choose your most likely variables and plug them into one of the many ballistic programs.

quote:

Originally posted by depusm12:
RHINOWSO

Would a 8"upper for 300 Blackout be too short to suppress . I'm looking at a pdw for home defense in a apartment. Or would a 10" 300 Blkout upper be better? If I wanted to stay with 5.56 would 10.5" or 11" upper be better?


James

This is my 8" 300blackout. It suppresses well. I don't have a chrono, but most by most accounts it should generate enough velocity and energy on supersonics to be very effective within 150 yards. Again, I haven't personally hunted or done ballistic testing, but the Hornady and Barnes 110 loads seem to be the favorite performers for expansion and accuracy. Accuracy of my particular build hasn't been tested any further. I shoot subs at the range for fun, they have significant drop in the same distance, some have had feeding issues. It has a full titanium suppressor made by Q that mounts on the brake, which is the blast baffle for the suppressor.

Sorry for the huge picture, I'll try to resize it.

10" Sig 516 G2 upper on a KAC SR15 lower, Law Tactical folder, SBA3 brace. I really like a piston in a short 5.56 because of how dirty and hot the DI guns tend to run. It does add some weight though.

Quick tangent - I'm using the same brake as Rustpot, but I'm not as cool as him and don't yet have a Trash Panda for it. Current rocking a Q Plan B adapter which mounts the Cherry Bomb to a SiCo Omega 30. Q's mounting system is the way.

As stated, it depends on the suppressor. I suppress 300 blk in 5” 8” 9” 12” and even 16” without issues.

As for a rifle for defense in an apartment...no way I’d do it, but that’s just me. I’m not sure I’d do much more than bird shot tbh.

Would a 9mm PDW be better for an apartment for home defense?

James

quote:

Originally posted by depusm12:
Would a 9mm PDW be better for an apartment for home defense?

Maybe? If your handgun shares mags with it, it might even be a better choice?

I built a DI "pistol" in 300blk for my HD/car use. It's got a 6" barrel with a Sandman-K suppressor.